1. Field of the Invention
The present invention relates to depositing films, and more particularly to an apparatus for preparing thin films by an oblique collimator deposition.
2. Description of the Prior Art
Sputtering is a commonly used method for thin film deposition. Sputtering is performed by providing ionized atoms, such as Ar+, in a vacuum which accelerate towards and bombard a negatively-charged target material. The ionized atoms knock off other atoms and molecules from the target material. These ejected atoms and molecules subsequently deposit on a pre-selected substrate also disposed in the vacuum chamber, thus forming a film on a surface of the substrate.
The trajectory of the ejected atoms and molecules depends in significant part on the incident angle of the bombarding ions and the scattering of ejected atoms and molecules as they collide with other particles. The trajectory follows a well-known cosine (or Gaussian) distribution. Therefore, the atoms and molecules directed towards the substrate surface come from various angles, and only a comparatively small portion are incident substantially perpendicular to the substrate surface. As a result, it is difficult for sputtering to achieve a deep conformal coverage within high aspect ratio steps or contacts on semiconductor wafer substrate.
To overcome this drawback, a device known as a collimator is used. A collimator, such as is diagrammatically represented in FIG. 1A with reference numeral 12, is placed between a target 10 and a substrate 15. Substrate 15 is generally bonded or clamped on a substrate holder 14. The chamber housing 16 is evacuated with a pump assembly (not shown). Collimator 12 typically comprises a disk-shaped object having a plurality of holes or openings 20 provided therethrough. The collimator functions effectively as a filter, allowing only the atoms and molecules 13 incident perpendicular to the substrate 15 to pass through and coat the substrate 15. This results in a more conformal deposition within deep contacts than when a collimator is not used.
FIG. 1B is a detail of the collimator 12 from the deposition system as shown in FIG. 1A. The collimator 12 can be described by its aspect ratio H/D, where H is the depth of the collimator and D is the diameter of the holes. FIG. 1C is a plan view of the collimator 12, which consists of a plurality of holes or openings 20 (only several holes are shown).
However, the collimator, like everything else within a sputtering chamber, gets coated with the sputtering material. The accumulation of sputtering material effectively diminishes the diametric size of the openings, thus reducing the deposition rate on the substrate. Eventually the amount of material able to pass through the openings may become unsatisfactory. Fortunately, there are techniques available, such as described in U.S. Pat. No. 5,409,587 to Sandhu, et al., to remove the accumulated materials and clean the collimator so that the sputtering can continue in a desired manner and deposition rate.
Existing techniques involving a collimator are effective in making the incident flux perpendicular to the substrate surface, but no such technique is available to make the incident flux oblique to the substrate surface (i e. an oblique sputtering deposition).
Actually, an oblique evaporation deposition technique was reported as early as in 1959 by Smith [D. O. Smith, J. Appl. Phys. 30, 264(1959)] and Knorr et al. [T. G. Knorr and R. W. Hoffman, Phys. Rev. 113, 1039(1959)] in 1959. The formation mechanism, micro-structure, texture, and anisotropy of the films evaporated at oblique incidence have been investigated by Smith et al [D. O. Smith et al., J. Appl. Phys. 31, 1355(1960)]. Hara et al. have studied the magnetic and optical anisotropy in obliquely rf sputtered iron and cobalt films [K. Hara et al., J. NIMM 116,441(1992)]. They found the magnetic anisotropy in iron film mostly originates from the shape anisotropy of crystallites, and that in cobalt film mostly originate from the magnetocrystalline anisotropy. At present, oblique evaporation deposition has found several applications, such as metal recording tape.
Oblique evaporation deposition is easier to achieve than oblique sputtering deposition. This is because oblique evaporation deposition is performed under a high or ultrahigh vacuum, and subsequently the directions of the evaporated particles can be controlled due to the large mean free path. In other words, there is less scattering because the mean free path is large. Oblique sputtering deposition is generally carried out under 10xe2x88x923 Torr vacuum, a lower vacuum than evaporation deposition, and accordingly the directions of the sputtered particles are hard to control because of the smaller mean free path (i.e. more scattering). Because of this, oblique sputtering deposition is seldom reported. More so, there is no existing device for preparing thin films on a whole disk substrate to produce columns of film material angled in the circumferential direction or radial direction by using oblique sputtering deposition.
The exemplary embodiments of the present invention overcome the foregoing and other problems by providing a device for preparing thin films by oblique sputtering deposition by inserting an oblique collimator between the target and the substrate. The exemplary embodiments of the present invention also provide a device for preparing thin films by oblique deposition by inserting an oblique collimator between the incident source and the substrate. The oblique collimators described herein enable preparing thin films with an angled column structure and in some embodiments adjustable angle.
The present invention includes a device for depositing a film onto a surface of a substrate. The device can have a film material source for dispersing film material incident in the general direction of the substrate surface. The device can have a collimator between the film material source and the substrate. The collimator can have passages therein which are angled obliquely relative to the substrate surface such that incident film material traveling toward the substrate in a trajectory which is not substantially parallel to the oblique angle of the passages is blocked.
These and other objects and advantages of the device according to the present invention will become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in various drawing figures.